1. Field of the Invention
This invention relates to an improved blade seal for use in a shearing blind ram for a ram-type blowout preventer used in oil and gas drilling operations. Ram-type blowout preventers are part of a pressure control system used in oil and gas drilling operations to control unexpected well bore pressure spikes or "kicks" as they are commonly referred to in the industry.
The blowout preventer has a body with a vertical bore and a pair of laterally disposed opposing bonnet assemblies. Each bonnet assembly includes a piston which is laterally moveable within the bonnet assembly by pressurized hydraulic fluid. Replaceable sealing elements called "packers" are mounted on the ends of the pistons which extend into the blowout preventer bore. When these pistons are moved to a closed position, commonly referred to as "closing the blowout preventer" or "closing the rams", the vertical bore of the blowout preventer is sealed and the "kick" is contained. These "packers" are available in a variety of configurations designed to seal the blowout preventer bore when the opposing pistons are moved to their closed position. One type of packer has ends designed to seal around pipe of a specific size in the blowout preventer bore when the blowout preventer is "closed." Other rams are designed to shear through a drill pipe extending through the vertical bore and seal off the bore. It is this type, commonly referred to as "blind shear" rams and the blade seal to be used therein to which the present invention is directed.
These shearing blind rams face a formidable task. They must be able to shear through a piece of drill pipe in the blowout preventer bore and then seal against each other to contain the well bore pressure during a "kick". The shearing blind rams must form a pressure tight seal during a kick until the well bore pressure can be controlled. The well bore pressure can reach several thousand pounds per square inch during a "kick." The shearing blind ram has various rubber seal elements attached to it to ensure a complete seal of the blowout preventer bore.
These seal elements, including the blade seal of the present invention, are exposed to tremendous well bore pressures. The blade seal of the current invention offers a substantial improvement by offering a simple, easy to manufacture blade seal that minimizes wear and tear of the elastomeric seal element.
2. Description of Related Art
Various types of shearing blind rams with various blade seals have been shown and used.
U.S. Pat. No. 4,537,250 to J. N. Troxell, Jr. shows a shearing ram utilizing a pair of hardened points to aid in initiating the shearing action. A plain rectangular seal acts as a blade seal.
The shear ram apparatus shown in U.S. Pat. No. 4,540,046 to S. W. Granger et al. discloses a blade seal with the rubber element bonded to a metal member.
U.S. Pat. No. 5,360,061 to L. M. Womble shows a blowout preventer with tubing shear rams designed to control the shape of the sheared pipe end.
U.S. Pat. No. 5,713,581 to D. W. Carlson et al. shows a blade seal of nitrile rubber with uniformly dispersed synthetic, non-cellulosic fibers to aid in preventing seal rollover.